Telephone-exchange apparatus



(No Model.) 4 shedssheet 1.

T.'B. DOOLITTLE.' TELEPHONE EXCHANGE APPARATUS. -Y No. 298,588. Patented May 18, 1884..

(No Model.) 4 sheets-,sheet 2.

T. B. DOOLITT-LE.. TELEPHONE EXGHANGE APPARATUS.

No. 298,559.' Patented May 13, 1884.

4 Sheets-Sheet 3,

T; B. DOOLTTLE TELEPHONE EXCHANGE APPARATUS.

(No Model.)

Patented May 13, 1884.

mi NQA )y AA WITNESSES NA PETERS, Fholo-Uihagmphor, Wishingon, D. Q

(No Model.) 4 Sheets-Sheet 4.

T. B. DOOLITTLE. TELEPHONE EXCHANGE APPARATUS.

Thoma/3 P, Z300i/Libie, Wd? 5% Patented vMany 13, 1884.

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OOOOOOOO O i l Y ga, @25AM/ llnrrnn Sfrafrns Partnr @maca THOMAS B. DOOLITTLE, OF BRIDGEPORT, GONNECTICUT.-

TELEPHONE-EXCHNGE APPARATUS.

SPECIFICATION forming part of Letters Patent No. 298,559, dated May 13, 1884. Application filed September 1G, 188i. (No model.) Patented in England February 1l, 1882, No. 661.

To all whom zit-may concern:

Beit known that I, TnoMAs B. DooLIrTLn, a citizen of the United States, and a resident of Bridgeport, in the county of Faireld and 5 State of Connecticut, have invented certain new and useful Improvements in Telephone- Exchange Systems and Apparatus, of which the following is a specification.

My invention relates to that system of telephonic intercommunication for private and 2o tervention of the central oiiice with which he is immediately connected, be placed in direct communication with any other subscriber who is connected in like manner with such central office, which is technically termed, an exchange-office.77 ln the application of such a system to large towns and cities there must necessarily be great numbers of individual subscribers provided with telephonieinstruments. The place where these subscribers are situated will hereinafter be designated as sub-stations,7 each of which must be capable of being placed in direct communication with any other at short notice whenever required. Under these conditions, however, experience has shown that the assembling together ofso many independent lines at one place and the greater frequency of calls for connection between different subscribers, which increase in much greater proportion than the increase in the 4c number of subscribers of sub-stations, gives rise to serious difficulties and delays in performing the service of making the connections, and thus greatly diminish the economy, eiiiciency, and general utility ofthe system.

The object of my invention is to diminish the hereinbefore mentioned inconveniencies by distributing the lines converging toa central station into dillerent groups, each group containing such a number of lines as experi- 5o ence shows may be conveniently attended by asingle operator, so that each such group ofv lines constitutes in effect an independent cenerations of the general system, and theseA should by preference be situated in the neighborhood oi' those centers of different branches of business which are usually found in all large commercial cities. Fach of these auxiliary central stations will serve a group of subscribers located in that particular geographical subdistrict whose private or individual lines will terminate therein. The-se auxiliary exchanges are each provided with a switch-board, and are connected with each other and with the principal centralstation by trunk-lines arranged upon the same principle as hereinbefore described.

My invention comprises certain improvements in construction of switch-boards, switches, and apparatus for establishing the connection between different lines, so that the same may be effected with the utmost convenience and celerity.

In the accompanying dra-wings, Figure l is a perspective view of a switch-board and operators table embodying my improvements. Fig. 2 is a side elevation, partly in section, of the signaling and connecting apparatus of one of the compartments ofthe switch. Fig. 2A is a detached view of a portion of the same. Fig. 3 is a front and Fig. et is a rear elevation of the same. Fig. 5 is a diagram illustrating the arrangement of the electrical connections in the switch-boards. Fig. 6 is a diagram illustrating the connections between different switch-boards in the same and in different ofiices, and Fig. 7 is a diagram of connections.

he switch-board represented in Fig. 1 is designed to be located at a central station and to accommodate a maximum number of fifty subscribers or sub-station lines, which is usually found to be as' great a number as can be conveniently attended by a single operator. The switch-board consists, preferably, of an upright case, A, the upper portion of which is IOO divided into boxes or compartments B B. In the drawings I have shown seventy-fivc of these compartments, arranged in three rows of twenty-five each, one above theother, the upper one being reserved especially for trunk and connecting lines. Each compartment may conveniently be about three and a half inches in height and one inch in breadth, and about four inches in depth from front to rear. Each one of these compartments is appropriated to a particular line, either a substation line or a trunk-line extending from another switchboard, as the ease may be, and itcontains all the special apparatus pertaining to that parti cular line.

C is the operatorfs table, which may be attached to the case A, containing the switchboard, and project horizontally in front of it, as represented in Fig. l, which is the arrangement I prefer; or it may, if desired, consist of a detached table. Upon this table are mounted the connecting devices for establishing com munication between one line and another, and

.operator or attendant in conversing with the subscribers and in making connections.

The special apparatus belonging to each individual line consists of a visual signal or annunciator for receiving signals, a key for transmitting signals, and a spring-jack or device whereby the connections with other lines are formed. I will now describe these special devices in detail, it being understood that the apparatus in each compartment of the switch* board is precisely similar to that in every other one.

The several parts of the apparatus are attached to a metallic frame, which, for the sake of economy and convenience, I prefer to form of a single castiug,consisting of a vertical faceplate, a, (see Figs. 2, 3, and 4,) having horizontal rearward extensions, a a2, from the latter of which extends vertically an angular bracket, ai.

D is an electro-magnet, which is mounted upon the upper rearward extension of the frame a?, and which has an armature, d, pivoted at d', and provided with a counter-balance, d?, of a weight just sufficient to overbalance the armature d and raise the same from the poles of the electro-magnet D when no electric current is traversing the latter.

E is an annunciator-drop or visual signal, which I prefer to construct in the manner illustrated in Figs. 2 and 3, it being pivoted` by its lower edge at the point e, which point, being in the rear of its center of gravity, gives the drop a tendency to fall forward through an angle of about forty-five degrees until stopped by the coming in contact of its beveled lower edge, c', with the face of the plate e. The drop E is normally held in this position of unstable equilibrium by means of a detent, c, which is affixed thereto, and projects rearwardly through a slot in the faceplate, so as to take hold of the edge ofthe slot Z3 in the armature d. rlhus it will be understood that when an electric current traverses the electromagnet D the armature d is attracted, and, being drawn down toward the poles of the electro-magnet,is disengaged from the detent c?, which action permits the drop E to fall forward, as hereinbefore explained. In Fig. l four drops are shown tilted forward in this position.

F is a key for transmitting signals, which is pivoted at f to the metallic frame a2, and is normally held by the pressure of an insulated spiral spring, f, against an insulated contact-point, g, which is termed its resting contact. lVhen the key is depressed, its contact with the point g is broken and a new one formed with another insulated contact-point, h, beneath it, which is termed the workingcontact.7

J is a peculiar form of circuit-changer called a springjack,7 which consists of a metallic bar, j, pivoted at j' to an insulated support,

while its free end rests in a seat, jg, formed of insulating material. A contact-spring, ja, is attached to the under surface of the bar j,and this normally rests against a similar contactspring, jl, attached to and in electrical connection with the frame a. At the rear ofthe metallic frame is attached a plate of insulating material, G, upon which are mounted four binding-screws. In Figs. 4L and 5 these are respectivelyT numbered l, 2, 3, and 4. The connectingwires from these binding-screws are run as follows: (Refer to Figs. 2 and 5.) No. 1 is connected by wire w with thespringjack j; No. 2 by the wire 102 with the working-contact 7L; No. 3 by the wire w3 with the resting-contact point g, passing through the coils of the electroanagnet D; No. 4 by the wire w'L with an insulated spring, II, which,

IOO

when required, is employed to establish a con nection with an audible signal or electric bell, I, common to all the lines, which may be mounted upon the case containing the switch, as shown in Fig. l, or may be placed in any other convenient locality. This bell or alarm is not in all cases an essential portieri of the apparatus, as the sound caused by the falling of the annunciator-drop will usually besu'liicient tonotify the operator or attendant that a signal has been transmitted from one of the sub-stations. station is attached to the binding-screw No. l in its appropriate compartment. The bindingscrew No. 2 of each compartment is united to a wire leading to one pole of a battery common to all the lines, the other pole of which is to earth. Binding-screw No. 3 of each compartment is attached to a wire leading directly to the earth, while to binding-screw No. 4 is connected a local battery or branch of the main battery for operating the special audible signal hereinbefore referred to.

y The normal circuit of each mainline may bc traced through its corresponding annunciatorcompartment in the switch-board as follows .Entering at the binding-screw 1, it passes to IIO upon similar studs,t t.

the spring-jackJ, and thence through the conl tacts js and j* to theframeaac, thence through the key F to the contact-point g, through the coils of the electro-magnet D to binding-screw No. 3, and thence to the earth.

I will now proceed to describe the device for establishing communication at the switch between two independent sub-station lines.

The operators table C (seen in Fig. l) is provided with a number of switch cords or connectors. Fach connector is made up of two lengths of iiexible conducting-cord united by intervening stationary conductors, as seen at L and L in Figs. l and 7. The arrangement will be best understood by reference to Fig. 7, which exhibits a section of a portion of the operators table, together with a theoretical diagram of the electrical connections.

S and S are two metallic thimbles,which are inserted in suitable apertures passing through the top of the table C,with their upper edges projecting a little above its surface.

The cords L and L each consist of a ilexible metallic conductor, which is provided with a non-conducting covering braided or woven upon it. One end of the cord L is attached by means of a screw, p, to the switch-pin P, which is a wedge of metal of the form shown in Fig. 2, which is preferably provided with an insulating-handle, whereby it may be conveniently manipulated. The switch-pin P normally rests upon the metallic thimble S, and the conducting-cord L, connected therewith, passes down through an opening within the thimble, its opposite end being attached beneath the table at n to one oi' the arms of the double-circuit changer N. The flexible conductor L is made long enough to hang in a loop, and a weight, llI, is hung upon the bight of the conductor, as shown in Figs. l and 7, thus tending to keep the switch-pin P in firm contact with the metallicthi mble S. The other flexible conductor, L', in like manner passes through the thimble S, and is attached in precisely the same manner to the other switchpin P by means of a screw, p. This conductor also carries a weight, M', and is attached at its opposite extremity to the other arm of the circuit-changer N. The two arms of the circuit-changer N are linked together by an insulating connecting-bar, @,which may be provided with a pin or handle for convenience of manipulation. Then this circuitchanger is in its normal position, its respective arms rest upon two metallic studs, o 0,which are united beneath the table by a conductingwire, 7, as indicated by the dotted line in Fig. 7. Then in this position a continuous electrical connection exists between the twoy switch-pins, P and P, by means of the cords L and L and the circuit-changer N. Then the circuit-changer N is shifted to the right, its arms are ,removed from o o and placed The last-named studs are connected by wires w8 and w" with theterminals of a telephone, T, which may be used. either for transmitting or receiving oral communications, or a separate transmitter and receiving-telephone may be employed, if prefer-red. The thimbles S and S- are connected with each other and with the earth aipQX by means of wires 105405. l

As hereinbefore stated, there is a number of independent connecting conducting-cords upon each operators table, each one of them being arranged in the manner` just described. In Fig. l I have shown six of these conductingcords, each provided with its own circuitchanger N, switch-pins P and P', cords L and L, and weights M and M. The telephone T is, however, common to all the conductors. Its respective terminal wires w8 and wf' are united with the corresponding studs throughout the series of six circuit-changers, N N, so that when any one of them is turned to the right the telephone will be switched into the particular connecting-circuit to which that circuitchanger appertains. The several thimbles S S S S', hereinbefore referred to, are all likewise in electrical connection with each other and with the earth/ as shown in Fig. 7

The diagram, Fig. 6, illustrates the manner in which different switch-boards in the same office or in different offices are connected with each other by the trunk lines, I prefer to reserve the upper row of compartments in each switch-board for the trunk and connecting lines', the remaining two rows being devoted to individual subscribers lines. In Fig. 6 I have shown two central stations, each having two switch-boards and one central station with a single switch-board. The four bindingscrews in each compartment oi' each switchboard are 'arranged in the manner hereinbefore described. The several line-wires entering the station are each connected to the binding-screw No. l of their respective compartments. The trunk or connecting lines are in like manner so arranged as to unite the binding-screw No. l in the proper compartment of one switch-board with the binding-screw N o. l of a corresponding compartment of the other switch-board, as will be clearly understood by reference to Fig. (5. The number of trunk or connecting lines between different switch-boards will of course be determined by the extent of intercominunication which is found to be required between subscribers connected with different boards. The trunklines connecting different. central oices are arranged upon the same general plan as those connecting differentswitch-boards in the same o'iiee, with the exception that in large exchanges it will be more convenient to devote one or more entire switch-boards to the trunkline connections and place that in charge of a special operator. In small exchanges apart of one of the ordinary switch-boards, as illustrated in Fig. 1, will be sufficient to accommodate all the trunk-line connections required.

In order to illustrate the pgractical operation of my improved system, I will iirst describe the process of establishing communication between two sub-stations connected with the IOO IIO

same switch-board, and afterward between two sub-stations connected with different switchboards. For example, if sub-station No. 15 wishes to communicate with sub-station No. 49, he rst transmits a call-signal by means of his battery, magneto-generator, or other equivalent device, which signal passes through compartment N o. 15 and releases the drop of the annunciator, allowing it to fall forward, as shown in Fig. 1. The operator at the table C inserts one of the switch-pins into the springjack of compartment No. 15, as shown, and then moves the corresponding circuit-changer N to the right, which brings the telephone T into the circuit. The circuit of line No. 15 now passes from the line-wire to the springjack, thence through the connecting-cord to the telephone, and from the telephone, through the other portion ofthe connecting-cord,to the other switch-pin,which rests upon one of the metallic thimbles, and is therefore in connection with the earth. The operator or attendant, by making use of the telephone T, ascertains that No. 15 wishes to communicate with No. 49; he accordingly removes the second switch-pin of the pair from the thimble on which it rests, thus breaking connection with the earth, and inserts it in spring-jack No. 49, still keeping his telephone in the connecting circuit until he learns that the correspondents are in communication with each other. He then turns his circuit-changer N to the left, thus removing the central-office telephone from the circuit and leaving the two lines in direct connection with each other through the circuit-changer N and flexible conductors L and L, as shown in Fig. 1. If the connection is to be made between two substations which are connected with different switch-boards-for example, .between No. 31 and a substation on switch-board N o. 2-the operation is the same as that last described up to the point of inserting the second switchpin,before doing which the operator at switchboard No. 1 rst presses the key F in that compartment of his switch-board which communicates through one of the connecting-wires with switch-board No. 2. This completes acircuit from the signaling battery or generator R (see Fig. 5) through the binding screw 2 and the key F, thence through the frame and spring-jack j to the binding screw 1, from whence it traverses wire w to the annunciator No. 1 of board No. 2. The signaling-current operates this annunciator and passes to the ground in precisely the same manner as a signal received from an individual subscriber. After signaling the operator of the second switchboard in this manner, the operator of the first switch-board places the second switch-pin in the spring-jack of the compartment through which he signaled the second switch-board,and by his telephone, which is now looped between the line from whence the call proceeded and the extension of the same between the switch boards, informsthe operator thereof of the designating name or number of the sub-staboard, each operator restores the annunciatorv drop to its normal position, and leaves the charge of the united circuit in the hands of the operator making the last connection. This operator, upon learning that the correspondence has terminated, transmits a call-signal by depressing the proper signal-key, which traverses the connecting or trunk line to the first switch-board. This action releases all the annunciator-drops of the compartments through which the connection .has been made, thus notifying the several operators to restore all the connections to their normal position. When, for any reason, the constant attention of an operator is not required at the switchboard, a single battery or other electric generator may be connected with the bindingscrews No. 4 of each compartment, which may be made to sound an electric alarm-bell whenever any one of the annunciator-drops falls forward and closes the circuit through its contact-point and spring.

I claim as my invention- IOO 1. In a telephone central-cnice system in which the incoming lines are connected in groups withaseries of sectional switch-boards, the combination, with the said sectional switchboards, of a'series of connecting-conductors extending between the switch-boards, vand provided at each terminal with devices for transmitting and receiving signals, and with connecting devices whereby call-signals or communications may be electrically exchanged between any two switch-boards or between sub-stations connected by main lines with any two switch-boards. v

2. The combination, substantially as hereinbefore described, of a series of sectional switchboards, a series of main lines divided into groups between the said switch-boards, a series of independent connecting-conductors eX- tending between each switch-board and every other switch-board, each of the said conductors being provided at each terminal thereof with signaling devices and circuit-connections, and a series of local connectors at each switchboard, each provided with a circuit-changer, whereby atelephone common to the series may be connected in circuit with any one of the series, whereby each switch-board is enabled to signal and communicate with every other switch-board, and wherebya line terminating at one switch-board may be interconnected with a line terminating at another switchboard, for the purposes specified.

3, The combination, substantially 'as here- IIO inbefore set forth, of a visual signal, an elcc tro-magnet for causing the same to be actuated or exhibited, a key provided with a resting and a working contact, a spring-jack having4 one of its terminals connectedy directly to a line-wire and its other terminal to the level' of said key, a connection from the restingcontact of said key to the earth, which includes said electro-magnet, and a connection from Athe working-contact of said key to one pole of an electric generator whose remaining pole is connected to the earth.

4. The improved spring-j ack, constructed substantially as hereinbefore set forth, consisting of a yielding metallic bar which normally rests in a non-conducting seat, a contact-point which forms an electrical connection with said bar while it rests in said seat, and a tapering metallic switch-pin which, when inserted between the yielding` bar and its non-conducting seat, forms an electrical connection with the said bar, and at the same time lifts it from the contact-point.

5. The combination, substantially as here-` inbefore set forth, of a non-conducting base, a metallic thimble inserted in said base and electrically connected with the earth, a ilexible conductor provided with a non-conducting envelope passing through said thimble, a metallic switch-pin or connector attached to and forming one terminal of said iiexible conductor, and a weight attached to or acting upon said iiexible conductor, tending to keep said terminal normally in electrical contact with said metallic thimble.

6. The combination, substantially as hereinbefore set forth, of a metallic thimble electrically connected with the earth, a exible] conductor provided with a non-conducting envelope passing through said thimble, a metallic switch-pin or connector attached to and forming one terminal of said iiexible conductor, and a weight attached to or acting upon said flexible conductor, tending to keep said terminal normally in electrical contact with said metallic thimble.

7. The combination, substantially as hereinbefore set forth, of two metallic thimbles electrically connected with each other and with the earth, two flexible conductors with nonconducting envelopes, said conductors passing through said thimbles, respectively, metallic switch-pins or connectors forming one terminal of each of said iiexible conductors, a telephone, and a circuit-changer for connecting the remaining terminals of said flexible conductors together, either directly or through said telephone.

8. The combination, substantially as hereinbefore set forth, of a metallic thimble, a iiexible conductor provided with a non-conducting envelope passing through said thimble, and a metallic switch-pin or connector attached to and forming one terminal of said ilexibleconductor, which terminal is larger than the opening ofthe thimble, whereby the terminalV is prevented from being drawn through the thimble by the tension of the conductor.

In testimony whereof I have hereunto subscribed my name this 14th day of September, A. D. 188i.

THOMAS B. DOOLITTLE.

Witnesses:

MILLER C. EARL,

GHARLns A. TERRY. 

